Members of this family adopt an alpha+beta sandwich structurewith an antiparallel beta-sheet, in a ferredoxin-like fold. Theyare predominantly found in plant cytokinin dehydrogenase 1,where they are capable of binding both FAD and cytokininsubstrates. The substrate displays a 'plug-into-socket' bindingmode that seals the catalytic site and precisely positions thecarbon atom undergoing oxidation in close contact with thereactive locus of the flavin [1]. Cytokinin dehydrogenase 1, FAD and cytokinin binding Cytokin-bind